Angioplasty procedures have gained wide acceptance in recent years as efficient and effective methods for treating types of vascular disease. In particular, angioplasty is widely used for opening stenoses in the coronary arteries although it is also used for the treatment of stenoses in other parts of the vascular system.
The most widely used form of angioplasty makes use of a dilation catheter which has an inflatable balloon at its distal end. Inflation of the balloon at the site of the occlusion causes a widening of the lumen to reestablish an acceptable blood flow thorough the lumen.
Often it is desirable to determine the severity of the occlusion in order to properly chose a dilation catheter. Various techniques have been used to determine the severity of the occlusion. One way of determining the severity of the occlusion is to measure pressure both proximal to and distal of the stenoses. Devices that are used for this purpose include catheter-like members with some type of pressure sensing device incorporated therein. One known device measures the pressure as a function of the deflection of a diaphragm located at either the proximal or distal ends of the catheter. Positioning the sensing part of the sensing device at the proximal end of the catheter can introduce measuring inaccuracies due to the catheter length. Positioning the sensing part of the sensing device at the distal end of the catheter requires the sensing device to be made extremely small. Otherwise, the sensing device will impede the blood flow and affect the pressure reading. It is desirable to provide a pressure sensor that is compact so that it can be delivered to narrow sites while having a high degree of accuracy.
Other known devices, for example, those disclosed in Delpy (U.S. Pat. No. 3,991,902) and Hok (U.S. Pat. No. 3,349,623), measure the change in capacitance or resistance caused by the displacement of a liquid/gas interface.